Method and apparatus for monitoring bit-error rate

ABSTRACT

A test set for evaluating network performance is described, and which may include an output device, a processor, a power supply, a memory unit, and a control terminal. The test set may be configured to receive a user-entered selection of one of a plurality of different bit-error rate profiles and generate a test signal exhibiting the selected bit-error rate profile. The test set may also supply the test signal exhibiting the selected bit-error rate profile to a network under test. In addition, the test set may receive as an input, an output from the network under test. The output may include the test signal exhibiting the selected bit-error rate. The test set may evaluate the received test signal and determine the performance of the network in response to the received test signal exhibiting the bit-error rate. The test set may then output the results of the evaluation.

BACKGROUND

When evaluating the performance of optical transport networks, it isoften necessary to monitor the bit-error rate (“BER”) and itsimplications on offering a given network service. The BER is the numberof bit errors occurring within a specified time interval. For example,BER can be expressed by the equation:

BER=N/T, where N is the number of bit errors and T is the time interval.

In practice, however, there are no universally agreed-upon values forthe parameters, N and T. Different network test platforms may monitorthe BER using different values, which makes it difficult to consistentlymonitor the BER. To make reliable measurements of system performance(such as protection switching times), it is necessary for the testplatforms to be flexible enough so that they can monitor the BER over awide range of values of N and T. Presently, no test platformsincorporate the flexibility to monitor the BER over a wide range ofvalues for N and T.

When evaluating the suitability of a platform for a given application(such as video transport, or other data transport applications) it mightbe necessary to generate a BER with a given combination of values for Nand T. The distribution of total bit errors N over the extent of periodT, is referred to as the BER profile. The ability to generate a specificBER profile is especially critical for systems that employ forward errorcorrection (“FEC”). All FEC techniques have limitations in the maximumnumber of contiguous bit errors they can correct. For example, suppose aparticular FEC algorithm is known to operate reliably under a BER of10⁻⁶ (1 error in 1 million bits). Given two profiles with the samenumber of bit errors over the same time interval, the FEC algorithm maybe perfectly capable of correcting bit errors for one BER profile, butnot another profile. FIGS. 1 and 2 illustrate two different BER profileswith the same total number of bit errors (N) over the same time interval(T) but with different error distributions over the time interval. Aparticular FEC algorithm may be able to correct errors for the profileshown in FIG. 1, but may not be able to correct the errors for the BERprofile shown in FIG. 2. This is a substantial problem for downstreamend-customers. For example, in the case of video transmission, anuncorrectable, rapid burst of a relatively small number of errors wouldresult in video quality degradations such as tiling.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a representation of a BER profile, showing distributions oferrors (N) over a time interval (T).

FIG. 2 is a graphical representation of a BER profile different from theprofile of FIG. 1, also showing a different distribution of errors (N)over the time interval (T).

FIG. 3 is a block diagram representation of a network under test andtest set consistent with a first exemplary embodiment.

FIG. 4 is a block diagram representation of an exemplary test setconsistent with the first embodiment.

FIG. 5 is a block diagram representation of an exemplary controlterminal consistent with the first embodiment.

FIG. 6 is a flowchart illustrating an exemplary method consistent withthe first embodiment.

FIG. 7 is a flowchart illustrating block 602 from FIG. 6.

FIG. 8 is a block diagram representation of a network under test andtest set consistent with a second exemplary embodiment.

FIG. 9 is a block diagram representation of an exemplary controlterminal consistent with the second embodiment.

FIG. 10 is a flowchart illustrating an exemplary method consistent withthe second embodiment.

FIG. 11 is a flowchart illustrating block 1002 from FIG. 10.

FIG. 12 is a flow chart illustrating of an exemplary method consistentwith a third embodiment.

DETAILED DESCRIPTION

Embodiments consistent with the present invention may be implemented ina test set configured to generate and output a test signal including aselected bit-error rate (“BER”) profile. In some embodiments consistentwith the present invention, the test set may also evaluate networkperformance in response to a selected BER profile supplied to a networkunder test (“NUT”). For example, to evaluate the robustness of a forwarderror correcting (“FEC”) algorithm, the test set may generate bit errorsin accordance with a selected BER profile. Embodiments consistent withthe present invention may allow the test set to generate not just a testsignal (such as a bitstream) with a constant number of bit errors overan entire time interval, but also a unique BER profile. Depending on thecharacteristics of the optical link between the network elements and theparticular data transport standard under consideration (e.g. SONET, SDH,etc.), some of the common BER profiles may be preprogrammed. Inaddition, embodiments consistent with the present invention may beimplemented with non-optical data transport networks, such as electricaland wireless networks.

As shown in FIG. 3, one embodiment consistent with the present inventionincludes a system 300 that comprises: a test set 302 (which may output atest signal including a user-selected BER profile); a monitoring unit314; and a NUT 304. The NUT 304 may include networks element 306 and308, and two optically protected lines, 310 and 312. Optically protectedline 310 may be a “protect” line and optically protected line 312 may bea “working” line. The NUT 304 in FIG. 3 is preferably an opticaltransport network, and includes two network elements, but may includeother, or additional network components. Examples of other networkcomponents include, but are not limited to, SONET/SDH add-dropmultiplexers, dense wave division multiplexing (“DWDM”) terminals,multi-service provisioning platforms (“MSPPs”), and multi-functionaccess devices (“MFADs”).

In this configuration, test set 302 is connected to NUT 304 via anoptical connection line 316. However, communication between test set 302and NUT 304 is not limited to optical transmission lines, and may beperformed by any suitable means including, but not limited to,electrical communication such as DS-1/Ds-3 or 10/100/1000 Gbps Ethernetand wireless communication.

Test set 302 may also be connected directly to NUT 304. FIG. 3 shows theoutput of NUT 304 connected to monitoring unit 314 via connection line318. Like connection line 316, connection line 318 is an opticaltransmission line, but it is not limited to optical transmission lines.Monitoring unit 314 may, however, communicate with NUT 304 by anysuitable means as is known. In addition, monitoring unit 314 may also beconnected directly to NUT 304.

Monitoring unit 314 may receive performance information from the outputof NUT 304, evaluate the performance of NUT 304 in response to the testsignal exhibiting the selected BER profile supplied to NUT 304, andoutput results of the evaluation. Performance information may indicatehow NUT 304 performs in response to a supplied test signal exhibitingthe selected one of a plurality of BER profiles. For instance, systemperformance information can be application specific and may indicate howan error correction algorithm executed by NUT 304 performs in responsethe selected BER profile. System performance information may representthe number of errored frames for a video transport application or thenumber of errored or dropped packets for any other data transportapplication.

FIG. 4 shows a more detailed representation of test set 302. Test set302 may include an output device 402, a processor 404, a power supply410, a memory unit 408, and a control terminal 406. Test set 302 mayalso include an input device 412, which may be used to load BERprofiles. Test set 302 may also be configured to receive power from anexternal power supply 418. Control terminal 406 may include a display502 configured to display the results of the network performanceevaluation.

In FIG. 4, output device 402 is connected to connection line 316, but itmay be connected to any suitable means for communicating with NUT 304.Output device 402 may also be configured to connect directly to NUT 304.Output device 402 may be, for example, an output port.

Power supply 410 may be a direct current power supply that supplies DCpower to the components in test set 302 (connections not shown). Powersupply 410 may take the form of batteries, rechargeable batteries, orany other appropriate dc power supply as is well known. Optionalexternal power supply 418 may be connected to test set 302 by anysuitable means as is well known, such as a power cord. External powersupply 418 may supply either AC or DC power to test set 302.Furthermore, external power supply 418 may replace power supply 410, ormay be used to supplement or complement the output of power supply 410.

Memory unit 408 may be connected to processor 404 and input device 412.Memory unit 408 may, however, be connected only to processor 404 or onlyto input device 412. Memory unit 408 may be any appropriate type ofmemory component, including, for example, ROM, PROM, RAM, EEPROM, Flash,etc. Memory unit 408 may store a plurality of different BER profiles.BER profiles may be input into memory unit 408 by processor 404, inputdevice 412, or both. BER profiles may also be preloaded into memory unit408 before assembly of test set 302. Memory unit 408 may include aremovable module so that BER profiles can be loaded into test set 302 bysubstituting a different memory component.

Input device 412 may be connected to memory unit 408 and processor 404.Alternatively input device 412 may be connected only to memory unit 408or only to processor 404. Input device 412 is configured to receive BERprofiles uploaded from any suitable BER profile uploading device. Forexample, input device 412 may be configured as a parallel port, serialport, JTAG, etc. BER profiles may be sent from input device 412 toprocessor 404, memory unit 408, or both, depending on the configurationof test set 302.

Processor 404 may be connected to output device 402, input device 412,memory unit 408, control terminal 406, and power supply 410 (connectionsnot shown). Processor 404 may also be connected to external power supply418, if external power supply 418 is implemented. Processor 404 mayinclude internal memory 416, which may be used to store at least one BERprofile. Processor 404 may receive and process a user's selection of oneof a plurality of different BER profiles selected via control terminal406; generate and supply a test signal exhibiting the selected BERprofile to output device 402; retrieve BER profiles from internal memory416, memory unit 408, or both, based on the user's selection; supply atest signal exhibiting the selected stored BER profile to output device402; receive BER profiles from input device 422; and send BER profilesto memory unit 408 or its own internal memory 416.

Control terminal 406 may be connected to processor 404. Control terminal406 may be used to select one of a plurality of different BER profiles.Control terminal 406 may receive user inputs to select one of aplurality of different BER profiles by setting constant values for thenumber of bit errors (N) and the time interval (T). Control terminal 406may also receive user inputs to select one of a plurality of differentBER profiles by selecting a BER profile stored in either the processor's404 internal memory 416 or memory unit 408.

Control terminal 406 may receive a user's input to change the selectedBER profile to another, different BER profile. Control terminal 406 maybe configured with any appropriate means as is well known forinformation input, such as knobs, buttons, an LCD screen accepting userinput, or a wireless sensor.

FIG. 5 shows a representation of control terminal 406. Control terminal406 may include a display 502 and a control panel 504. Display 502 maybe any display, such as a liquid crystal display, CRT, etc. Display 502may display any information relevant to the operation of test set 302,such as the user-selected values for N and T (if the user has input suchvalues), the selected stored BER profile, or a list of stored BERprofiles for possible selection. The list may include graphic displaysof BER profiles. Control panel 504 may allow the user to makeselections, such as whether to enter values for N and T or to select astored BER profile. Control panel 504 may receive a user's entries orselections to be made in any appropriate manner as is well known, suchas a liquid crystal display recognizing user inputs, control knobs,buttons, etc.

FIG. 6 shows a flow chart depicting a process consistent with oneexemplary embodiment. The process begins with step 602, where the systemmay accept a user-entered selection of one of a plurality of differentBER profiles, using control terminal 406. Step 602 may include receivingselections of values for N and T, receiving selections of a BER profilefrom a plurality of stored BER profiles, or both. Next, in step 604,test set 302 may generate a test signal exhibiting the selected BERprofile. In step 606, test set 302 may output the test signal exhibitingthe selected BER profile.

FIG. 7 illustrates more details of step 602 from FIG. 6, where thesystem may receive a user-entered selection of BER profiles by eitherreceiving selections and entries of values for N and T or receivingselections of a BER profile from a plurality of stored BER profiles. InFIG. 7, step 602 may begin by receiving a user-entered selection. Atstep 702, the system may receive a user's choice of either enteringvalues for N and T or selecting a stored BER profile. Typically, controlterminal 406 receives the user's choice. Display 502 may prompt the userto select how he or she wants to select a BER profile. If the systemreceives an input indicating that the user wants to enter values for Nand T, control may proceed left from step 702 to step 704. At step 704,the system may receive selections or entries of values for N, and atstep 706, the system may receive selections or entries for values of T.FIG. 7 shows N selected before T, but T may be selected before N. If thesystem receives an input indicating that the user wants to select astored BER profile, control may proceed right from step 702 to step 708.At step 708, the system receives a user's selection of a stored BERprofile stored in test set 302. Typically display 502 displays a menu ofstored BER profiles available for the user to select. Once the systemhas received a selection for a BER profile, control may proceed to step604 in FIG. 6.

FIG. 8 shows a system 800 consistent with a second exemplary embodiment.Test set 802 may also be connected to the output of NUT 804 viaconnection line 818. A separate monitoring unit is thus not necessary.The connection between the output of NUT 804 and test set 802 may be byany suitable means as described above in the first exemplary embodimentwith respect to the connection between NUT 304 and monitoring unit 314.

FIG. 9 shows a more detailed representation of test set 802 configuredin accordance with the second exemplary embodiment. Test set 802 mayinclude an output device 902, a processor 904, a power supply 910, amemory unit 908, a control terminal 906, a first input device 912, and asecond input device 914. In addition, control terminal 906 may beconfigured with a display and control terminal similar to thosedisclosed in the first preferred exemplary embodiment. Test set 802 maybe configured similarly to the first preferred exemplary embodiment.Furthermore, unless described below, components commonly named in thefirst and second preferred exemplary embodiments may operate similarly.

Second input device 914 may be connected to processor 904. Second input914 may receive as an input, output signals representing networkperformance information from an output of NUT 804, and supply thereceived performance information to processor 904. Processor 904 mayreceive the performance information, evaluate the received performanceinformation, and output results of the evaluation. Processor 904preferably outputs results of the evaluation to control terminal 906.

FIG. 10 is a flow chart depicting a process consistent with the secondexemplary embodiment. The process begins with step 1002, where thesystem may receive a selection one of a plurality of different BERprofiles using control terminal 906. Specifically, at step 1002, thesystem may receive selections of values for N and T, receive selectionsof a stored BER profile, or both. Next, in step 1004, test set 802 maygenerate a test signal exhibiting the selected BER profile. At step1006, test set 802 may supply the test signal exhibiting the selectedBER profile to NUT 804. At step 1008, test set 802 may receiveperformance information from an output of NUT 804. Test set 802 may thenevaluate the received performance information to determine networkperformance at step 1010. At step 1012, test set 802 may output resultsof the evaluation. Preferably the results are output to control terminal904.

FIG. 11 represents more details from step 1002 from FIG. 10, where thesystem may receive a user-entered selection of BER profiles by eitherreceiving selections and entries of values for N and T or selections ofa BER profile from a plurality of stored BER profiles. In FIG. 11, step1002 may begin by receiving a user-entered selection. At step 1102, thesystem may receive a user's choice to either enter values for N and T orselect a stored BER profile. Typically, control terminal 906 receivesthe user's choice. A display, that may be the same as the one shown inFIG. 5, may prompt the user to select how he or she wants to select aBER profile. If the system receives an input indicating that the userwants to enter values for N and T, control may proceed left from step1102 to step 1104. At step 1104, the system may receive selections orentries of values for N, and at step 1106, the system may receiveselections or entries of values for T. FIG. 11 shows N selected beforeT, but T may be selected before N. If the system receives an inputindicating that the user wants to select a stored BER profile, controlmay proceed right from step 1102 to step 1108. At step 1108, the systemreceives a user's selection of a stored BER profile stored in test set802. Typically a display, that may the same as the one shown in FIG. 5,may display a menu of stored BER profiles available for the user toselect. Once the system has received a selection for a BER profile,control may then proceed to step 1004 in FIG. 10. Although the exemplaryembodiments describe specification of receiving a user-entered selectionof BER profiles by receiving either selections and entries of values forN and T or selections of a BER profile from pre-stored BER profiles,embodiments may be configured to allow a user to create a custom BERprofile by specifying different values for N over subintervals t over agiven time interval T.

FIG. 12 is a flow chart of a method representative of a third exemplaryembodiment consistent with the invention. The method shown in FIG. 12may be performed on NUT 804 by test set 802 from the second preferredexemplary embodiment. NUT 804 may execute a specific error correctingalgorithm. The error correcting algorithm may be known to operatereliably (i.e., correct a certain number of errors) under a certain BER.The error correcting algorithm may however, not be able to operatereliably for different profiles with the certain BER. For example,referring again to FIGS. 1 and 2, these figures show two examples of BERprofiles that may have the same number of bit errors (N) over the sametime interval (T), but with different combinations of N and T, and alsodifferent variations of the bit errors as a function of time. In thisexample, the error correcting algorithm may operate reliably for the BERprofile in FIG. 1, but not for the BER profile in FIG. 2.

In FIG. 12, steps 1202 through 1208 may be the same as steps 1002through 1008 in FIG. 10. From step 1208, control may proceed to step1210. In step 1210, the system may evaluate the received test signal todetermine the numbers of bit errors in the received test signal. At step1212, processor 904 may determine whether the numbers of bit errorsexceeds a predetermined threshold (i.e., the error correcting algorithmexecuted by NUT 804 cannot correct a specified number of bit errors). Ifthe system determines that the test signal exhibits numbers of biterrors exceeding the predetermined threshold, control may proceed tostep 1214. At step 1214, the system may store the parameters of thesupplied BER profile and an indication of the determination in memory.Parameters may be the values for N and T, including variations of N as afunction of time. The indication may represent whether the errorcorrection algorithm performed satisfactorily in response to the testsignal exhibiting the selected BER profile. The parameters andindication of the determination may be collectively known as “results.”“Results” include, but are not limited to, a pass/fail indication orindications and observed BER versus expected range for the test to pass.

Control may then proceed to step 1216. At step 1216, test set 802 mayreceive a selection of a BER profile different than the most recentlyselected BER profile. Preferably control terminal 906 receives a user'sentry to select a different BER profile. Alternatively, processor 904may select the BER profile by receiving and executing preloadedinstructions. The preloaded instructions may take the form of a computerprogram. The program may be written in any appropriate computerprogramming language. Once test set 802 receives an input to select adifferent profile, control may proceed back to step 1206.

If however, the system determines that the test signal exhibits numbersof bit errors that do not exceed the predetermined threshold, controlmay proceed to step 1218. At step 1218, the system may store parametersof the supplied BER profile and an indication of the determination.Parameters may be the values for N and T, including variations of N as afunction of time. The indication may represent whether the errorcorrection algorithm performed satisfactorily in response to the testsignal exhibiting the selected BER profile. The parameters andindication of the determination may be collectively known as “results.”Control may then proceed to step 1220. At step 1220, test set 802 mayoutput stored results. Test set 802 may output stored results to controlterminal 906.

In the preceding specification, specific exemplary embodiments have beendescribed with reference to specific implementations thereof. It will,however, be evident that various modifications and changes may be madethereunto, and additional embodiments may be implemented, withoutdeparting from the broader spirit and scope of the invention as setforth in the claims that follow. The specification and drawings areaccordingly to be regarded in an illustrative rather than restrictivesense.

1-22. (canceled)
 23. A method, comprising: generating a test signalexhibiting a selected bit error rate (BER) distribution profile; andproviding the test signal as input to a test network.
 24. The methodaccording to claim 23, further comprising: receiving from the testnetwork an output signal based on the input test signal; and evaluatingperformance of the test network based on the output signal.
 25. Themethod according to claim 24, wherein the test network generates theoutput signal by applying an error correction algorithm to the inputtest signal.
 26. The method according to claim 25, wherein the errorcorrection algorithm comprises forward error correction (FEC).
 27. Themethod according to claim 23, wherein the BER distribution profile isselected from a plurality of different BER distribution profiles. 28.The method according to claim 23, further comprising selecting a numberof bit errors and a time interval over which the bit errors aredistributed for the BER distribution profile.
 29. The method accordingto claim 23, wherein the test network is any one of an optical transportnetwork, an electrical transport network, and a wireless transportnetwork.
 30. A method comprising: selecting a bit error rate (BER)distribution profile from a plurality of BER distribution profiles;generating a test signal exhibiting the selected BER distributionprofile; and outputting the test signal.
 31. The method according toclaim 30, wherein selecting a BER distribution profile comprises:selecting a distribution; selecting a number of bit errors; andselecting a time interval over which the bit errors are distributed. 32.The method of claim 30, further comprising: receiving an input signalbased on the output test signal; comparing the input signal to theoutput test signal; evaluating performance based on the comparison; andoutputting a result of the evaluation.
 33. A method, comprising:selecting a bit error rate (BER) distribution profile from a pluralityof BER distribution profiles; generating a test signal exhibiting theselected bit error rate (BER) distribution profile; supplying the testsignal as input to a network under test; receiving from the networkunder test a corrected output signal based on the input test signal; andevaluating performance of the network under test based on the input testsignal and on the corrected output signal.
 34. The method according toclaim 33, wherein the network under test generates the corrected outputsignal by applying an error correction algorithm to the input testsignal.
 35. The method according to claim 34, wherein the errorcorrection algorithm comprises forward error correction (FEC).
 36. Themethod according to claim 33, further comprising receiving a selectionof a number of bit errors and a time interval over which the bit errorsare distributed for the selected BER distribution profile.
 37. Themethod according to claim 33, wherein the network under test is any oneof an optical transport network, an electrical transport network, and awireless transport network.
 38. An apparatus, comprising: a memorystoring a plurality of different bit error rate (BER) distributionprofiles; a control terminal for receiving a BER distribution profileselected from the stored plurality of BER distribution profiles; aprocessor generating a test signal exhibiting the selected BERdistribution profile; an output device supplying the test signal asinput to a network under test; an input device receiving from thenetwork under test a corrected output signal based on the input testsignal; and a monitoring unit evaluating performance of the networkunder test based on the input test signal and on the corrected outputsignal.
 39. The apparatus according to claim 38, wherein the correctedoutput signal comprises the input test signal corrected according to anerror correction algorithm.
 40. The apparatus according to claim 39,wherein the error correction algorithm comprises forward errorcorrection (FEC).
 41. The apparatus according to claim 38, wherein thecontrol terminal receives input from a user selecting a number of biterrors and a time interval over which the bit errors are distributed forthe BER distribution profile.
 42. The apparatus according to claim 38,wherein the network under test is any one of an optical transportnetwork, an electrical transport network, and a wireless transportnetwork.
 43. A method, comprising: generating a first test signalexhibiting a first bit error rate (BER) distribution profile selectedfrom a plurality of different BER distribution profiles; supplying thefirst test signal as input to a network under test; receiving from thenetwork under test an output signal comprising the first test signalsubject to an error correction algorithm; and determining a number ofbit errors in the output signal.
 44. The method according to claim 43,further comprising storing parameters identifying the selected BERprofile when the number of bit errors is less than a threshold.
 45. Themethod according to claim 44, further comprising repeating thegenerating, supplying, receiving, determining, and storing steps withrespect to a second test signal exhibiting a second BER distributionprofile when the number of bit errors in the output signal is not lessthan the threshold.
 46. The method according to claim 45, wherein: thefirst and second test signals have the same bit error rate; and theerror correction algorithm comprises forward error correction (FEC).